Poly(A) containing RNA was isolated from cells infected with type 3 parainfluenza virus. Actinomycin D was added to medium to abolish cellular transcription, and RNAs were resolved by agarose gel electrophoresis under denaturing conditions. Nine major poly A(+) RNA's that were estimated to be 0.3, 0.8, 1.4, 1.5, 1.7, 2.0, 2.5, 3.0, and 7.0 kilobases were visualized. Single stranded 32P labeled cDNAs were synthesized using mRNA's from infected cells and oligo(dT) as primer. When these cDNAs were analyzed by alkali agarose gel electrophoresis, discrete bands ranging in size from about 6000 to 300 bases were observed. The individual single stranded cDNAs were then made double stranded and cloned in E. coli by procedures described previously. In addition, RNA/DNA hybrids were cloned directly after dG/dC tailing. Full length cDNA recombinants large enough to represent DNA copies of individual transcripts were identified by serial colony hybridization. Several recombinants encoding different para-3 transcripts have been identified. Northern blot analysis, hybrid-selection and in vitro translation are currently being employed to identify the viral recombinants.